Field of the Invention
The present invention relates to a lift-off method for transferring an optical device layer in an optical device wafer to a transfer substrate, the optical device layer being formed on the front side of an epitaxy substrate such as a sapphire substrate and a silicon carbide substrate through a buffer layer.
Description of the Related Art
In an optical device fabrication process, an optical device layer composed of an n-type semiconductor layer and a p-type semiconductor layer is formed on the front side of a substantially disk-shaped epitaxy substrate such as a sapphire substrate and a silicon carbide substrate through a buffer layer. The optical device layer is formed of GaN (gallium nitride), InGaP (indium gallium phosphide), or AlGaN (aluminum gallium nitride). The optical device layer is partitioned by a plurality of crossing streets into a plurality of regions where a plurality of optical devices such as light emitting diodes and laser diodes are respectively formed, thus constituting an optical device wafer. The optical device wafer is divided along the streets to thereby obtain the individual optical devices.
Further, as a technique of improving the luminance of an optical device or improving the cooling thereof, Japanese Patent Laid-open No. 2004-72052 discloses a manufacturing method called lift-off for transferring the optical device layer of the optical device wafer to a transfer substrate formed of Mo, Cu, or Si, for example. The above-mentioned lift-off method includes the steps of bonding the transfer substrate through a bonding metal layer formed of Au—Sn (gold tin alloy), for example, to the optical device layer of the optical device wafer, next applying a laser beam having a wavelength (e.g., 257 nm) transmissive to the epitaxy substrate and absorptive to the buffer layer from the back side of the epitaxy substrate to the buffer layer, thereby breaking the buffer layer, and next peeling the epitaxy substrate from the optical device layer, thus transferring the optical device layer to the transfer substrate.